An air conditioner having a demand control function for reducing power consumption such that power consumption does not exceed a predetermined threshold value is known. A method of adjusting an expansion valve open degree according to an external demand command is known as a demand control method (refer to reference 1). This method reduces power consumption by controlling the quantity of refrigerant circulating in an air conditioning cycle. However, since the method cannot optimally control the air conditioning cycle according to air-conditioning load, power reduction effect is limited.
A method of controlling a compressor speed according to an external demand command is known as another demand control method (refer to reference 2). This method can improve COP by reducing the quantity of refrigerant circulating in an air conditioning cycle and increasing the efficiency of the air conditioning cycle. However, since the method cannot optimally control the air conditioning cycle according to air-conditioning load, power reduction effect is limited. Furthermore, this method may cause an air conditioner to operate at a cooling evaporation temperature/heating condensation temperature which damages comfort of a user environment.